1. Field of the Invention
The present invention relates to a method and apparatus for sensing the material of an object.
2. Description of the Related Art
Currently, material sensing apparatuses for sensing materials of objects have been receiving attention in various technical fields. For example, in printers, the number of types of paper used has been increasing year by year, and there is a demand for apparatuses which sense the type of paper (e.g., OHP sheets, glossy paper for photographs, coated paper, or plain paper).
For example, in an ink-jet printer, with the advances in ink-jet technology, it has become possible to print high-quality images, such as photographs. In such cases, control of the amount of ink ejected from the ink-jet printer toward the paper and control of permeation of ink by treatment of the surface of paper are important factors. In order to improve the control of the ink ejection amount, for example, ink ejection devices with a finer structure have been developed. The control of ink permeation has been improved by special coatings applied to the surface of paper for high quality images. Consequently, special-purpose paper for high quality images is used when a high quality image is printed, and plain paper is used for ordinary printing. Special-purpose paper is inevitably expensive because of its surface treatment. There are several grades in special-purpose paper depending on the extent of required image quality, and the price varies with the grade. As another type of printing media, transparent sheets for OHP are still used. As described above, various types of printer paper are used.
Since various types of paper are used, the setting of the printer parameters settings must be changed according to the type of paper. In the case in which a user changes a setting manually, if the user makes an error in selecting the type of paper or if the user fails to operate the paper setting properly, there is a possibility that simple characters are printed on an expensive special-purpose sheet for high quality images, thus wasting the sheet.
Currently, there is an increasing demand for means and apparatuses which sense the type of paper.
In a conventional apparatus for sensing the type of paper, which is built into commercially available ink-jet printers, the surface of a sheet is irradiated with light by a light-emitting element, and reflected light and scattered light are detected by a photo-detector. When the surface of the sheet is irradiated with a specific ray of light, reflected light and scattered light differ depending on the glossiness of the surface of the sheet and the surface roughness. The above-mentioned apparatus senses the type of paper using this principle.
However, in the apparatus described above, since the light emitting element and photo-detector are expensive, the apparatus itself becomes expensive. In order to enhance sensing accuracy, a light emitting element which emits short-wavelength light (e.g., blue light) and a photo-detector which detects such light are used. In such a case, the apparatus becomes even more expensive.